Dynamic Recrystallization Kinetics of As-Cast Fe-Cr-Al-La Stainless Steel during Hot Deformation

Abstract

To investigate the dynamic recrystallization (DRX) behavior of as-cast Fe-20Cr-5.5Al-0.64La stainless steel, a series of compression tests were carried out on a Gleeble-3500 thermal simulator in the temperature range of 1000~1150 °C and the strain rate range of 0.001~1 s−1. The true stress-true strain curves were obtained and their characteristics were analyzed. Using regression analysis, the apparent activation energy for the Fe-20Cr-5.5Al-0.64La stainless steel was estimated to be 300.19 kJ/mol, and the constitutive equation was developed successfully with a hyperbolic sine equation as: <!-- MathType@Translator@5@5@MathML2 (no namespace).tdl@MathML 2.0 (no namespace)@ --><math><mrow><mover accent="true"><mrow><mi>ε</mi></mrow><mo>˙</mo></mover><mo>=</mo><msup><mrow><mi>e</mi></mrow><mrow><mn>21.91</mn></mrow></msup><msup><mrow><mfenced open="&#x005B;" close="&#x005D;" separators="&#x007C;"><mrow><mrow><mrow><mi mathvariant="normal">sinh</mi></mrow><mo>⁡</mo><mrow><mfenced separators="&#x007C;"><mrow><mn>0.035</mn><mi>σ</mi></mrow></mfenced></mrow></mrow></mrow></mfenced></mrow><mrow><mn>3.18</mn></mrow></msup><mi mathvariant="normal">e</mi><mi mathvariant="normal">x</mi><mi mathvariant="normal">p</mi><mo>⁡</mo><mfenced separators="&#x007C;"><mrow><mfrac><mrow><mo>&#x2212;</mo><mn>300190</mn></mrow><mrow><mi>R</mi><mi>T</mi></mrow></mfrac></mrow></mfenced></mrow></math><!-- MathType@End@5@5@ -->. The critical strain, the peak strain and the strain for the maximum softening rate were identified based on the work hardening rate curves and expressed as a function of the Zener−Hollomon parameter. The kinetic model of DRX was established using the stress−strain data. According to the analysis of the kinetics model and microstructure evolution, the evolution of DRX volume could be described as follows: the volume fraction of DRX grains increased with an increase in strain; at a fixed deformation temperature, the DRX volume fraction was larger at a lower strain rate for the same strain; and the size of DRX grains increased with an increase in temperature or a decrease in strain rate.